In total knee arthroplasty, a damaged knee joint is replaced with a prosthesis to reproduce natural knee function. Multiple faceted cuts are made on the femur and at least one cut is made to the tibia to prepare the bone surface for application of the knee replacement prosthesis. These cut surfaces are preferably precisely angularly aligned to each other and are planar to enable satisfactory mating with the prosthesis.
In preparing the joint for a prosthesis, a series of cuts are made to the inferior end of the femur and the superior end of the tibia. Exemplary femoral cuts are depicted in FIG. 1. Initially the femur is cut to create a flat surface (annotated “A” in the drawings) generally perpendicular to the longitudinal mechanical axis of the bone. Next, two flat cuts are made generally parallel to the longitudinal mechanical axis of the femur: one at the rear of the knee to remove the posterior femoral condyles B and another at the front of the knee C. Lastly, two chamfered cuts D, D′ are made at approximately a forty-five degree angle at the juncture of the perpendicular and the anterior and posterior planes (or “planed femoral surfaces”). The superior end of the tibia is cut off perpendicular to the longitudinal mechanical axis of the tibia in a fashion similar to femoral cut A.
Skeletal joints are subject to high degrees of mechanical stress. The secure attachment of joint replacement structures to the bone is, therefore, critical in determining the long-term success of the surgical procedure. The accuracy with which the bone ends are shaped is essential to achieving a secure connection between the existing bone and an implanted prosthesis.
A number of studies have documented the correlation between imprecise bonding surface preparation and later complications for joint replacement patients. Knee implant malpositioning due to deficient bone resecting technique contributes to poor long-term results by influencing a prosthesis' function, load distribution, wear and fixation.
These discoveries have led researchers to propose standards that improve the likelihood of post-surgical success. Sandborn et al. recommended that the gap between the bone and a porous-coated knee implant not exceed 0.5 mm for optimal bone ingrowth. P. M. Sandborn et al., The Effect Of Surgical Fit On Bone Growth Into Porous Coated Implants, 12 Trans. Orthop. Res. Soc., 217 (1987). Cooke et al proposed a maximum cutting error of ±1 mm for proper bone fixation into a porous-coated prosthesis. T. D. Cooke et al., Universal Bone Cutting Device For Precision Knee Replacement Arthroplasty And Osteotomy. 7 J. Biomed. Eng. 45, 50 (1985). These levels of accuracy are currently difficult to achieve.
Unfortunately, these currently exists as much as a ten-fold discrepancy between the precision of the implant manufacturing tolerances (±0.2 mm) and the bone cutting process. Bone cements are often used to fill the gap between resected bone tissue and the prosthesis. Even with the use of bone cement, however, an uneven cement mantle due to poor bone cutting can result in early prosthesis loosening.
To aid the surgeon in making the precise multiple bone cuts required for this type of surgery, various guides and devices have been proposed. An initial group of devices are secured to the saw driver and to the patient and/or the surgical table. A second group includes cutting guides that guide the saw blade, typically within a close fitting slot.
The first group includes, for example, U.S. Pat. No. 4,457,307, issued to Stillwell, which discloses a bone cutting device for total knee replacements that is secured to the femur throughout its use. With this device, cuts are made both to the femur and the tibia. The Stillwell design requires removal of a large amount of soft tissue and a substantial number of calculations and adjustments in order to make the cuts required for total knee replacement surgery.
U.S. Pat. No. 4,574,794, issued to Cooke et al., discloses a guide for supporting a bone saw driver. The Cooke guide includes a complex system of parallel guide rods secured to the operating table as well as to the long bones of the leg and the bones of the foot. The device requires extensive fixation to the bone and numerous calculations to generate the desired cuts on the knee joint. U.S. Pat. No. 5,007,912, issued to Albrektsson et al., discloses a cutting device mounted to a frame. The frame is connected to the patient's femur and to the operating table. Similar to the Cooke device, this system requires extensive manipulation of the saw driver and the patient to create the required cuts.
U.S. Pat. No. 5,092,869, issued to Waldron, discloses a surgical saw guide, including retractable guide pins mounted in guide pin holders which stabilize the saw for translational movement along a linear axis.
U.S. Pat. Nos. 5,228,459 and 5,304,181, issued to Caspari et al., disclose an apparatus that is affixed to the tibia and the ankle that includes a rack and pinion mechanism to linearly advance a surgical milling device to make the appropriate surface cuts for total knee replacement surgery. The '181 patent discloses refinements to the device of the '459 patent.
U.S. Pat. No. 5,653,714, issued to Dietz et al., discloses a multi-component assembly that slides and pivots a milling head in order to make the cuts required for knee replacement surgery.
The second group of cutting guide systems includes devices such as that disclosed in U.S. Pat. No. 5,925,049, issued to Gustilo et al. The Gustilo patent discloses slotted cutting guides which are secured to the bone end by screws or other fixtures. Slotted cutting guides assist in orienting the blade of a surgical bone saw during the cutting process.
Despite these efforts, there remains room for improvement in the creation of precise and accurate bone cuts with current cutting technologies.
Devices that guide the saw body tend to be complex and cumbersome to set up, adjust and use. Orthopedic surgery is a physically demanding, labor intensive and time-consuming endeavor. Added instrument complexity tends to lead to longer procedures, which results in surgeon fatigue and a greater chance of surgical error.
Surgical cutting guides tend to obstruct the surgeon's view of the cutting site. This increases the risk of inadvertent damage to surrounding tissue, and can reduce the accuracy of a cut.
The oscillating saw used by orthopedic surgeons can be guided along a surgical cutting guide by hand. Some cutting guides utilize slots to provide a measure of blade control during surgery. There are numerous limitations with this cutting methodology. The very nature of resting an oscillating saw blade against another surface while the saw blade is in motion creates a certain degree of imprecision.
Also, to allow clearance for the saw in the kerf, surgical bone saw teeth are set. That is, alternate teeth are offset from the center of the blade so that the resulting cut is slightly wider than the blade, to prevent the blade binding in the kerf. Consequently, the guide slot must be wide enough to receive the set of the teeth. This creates enough clearance for the blade to toggle within the slot and substantially reduce the precision of the cut.
The surgeon's hand motions can cause the blade to toggle during the procedure and generate a non-planar bone surface. Vibrations generated by the oscillating saw driver are transmitted to the hands of the surgeon and to the cutting guide, affecting the quality of the resected bone surface.
In addition, inadvertent blade contact with the inner slot surface of a cutting guide dulls the blade teeth and damages the guide slot. Contact between the blade and guide can also result in a temporary loss of blade control. Consequently, it is difficult to maintain the saw oriented in the desired plane and angle.
Additionally, current cutting guide sets contain a large number of precision machined parts. These parts are expensive and their multiplicity creates both added expense and complexity. It would be preferable if the orthopedic surgeon had available a simpler cutting guide system with relatively few parts.
Thus, there is a need for a surgical saw guide that allows for the precise faceting of bone ends to facilitate the implantation of orthopedic prostheses. The guide should be simple to set up and use while creating precision planar cuts in bone tissue. It is preferred that the guide minimize saw blade damage and wear and that the guide minimize vibrational energy transfer to the surgeon's hands and the patient's bone. It would be preferable to minimize the amount of visual obstruction presented by the cutting guide.